Michelle Obama looked out across the sea of exuberant supporters wrapped up against the chill as midnight approached on the streets of Des Moines, and beamed.

It was the final rally of her husband’s final campaign for elected office and the First Lady allowed herself some nostalgia amid the cheerleading on the eve of the presidential poll.

Iowa was where Barack Obama’s seemingly implausible journey to the White House began with his caucus victory breakthrough at the turn of 2008. And this heartland state was now where the first African American president and his wife were making their closing plea for votes after a gruelling election contest.

Mrs Obama recalled house parties of supporters and the celebration of her oldest daughter’s birthday there, not to mention seeing her husband’s face carved in butter at a Christmas festivity, all as they criss-crossed Iowa during 2007.

And she thanked the state for the welcome that it showed her family, “especially our girls”, in that campaign.

Such support, she said, made a crucial difference “back in those early days when I wasn’t so sure about this whole process, back when I was still wondering what it would mean for our girls and our family if Barack got the chance to serve as president”.

The next night, the First Lady and her girls, Malia, now 14, and her sister Sasha, 11, joined Mr Obama on stage in Chicago to savour his re-election. It was the ultimate family party.

But as she acknowledged to that 20,000-strong crowd in Des Moines, she was not always enthusiastic about her husband’s aspirations for the nation’s top job, fearful of the turmoil it would wreak on their family life.

She overcame those doubts to become one of Mr Obama’s most powerful political weapons during his ugly election battle with Mitt Romney, the Republican challenger.

And even as the two campaigns plumbed new depths of vitriol and attack, Mrs Obama delivered an upbeat interpretation of the president’s legislative achievements and his personal character as a husband and father.

She made scores of solo campaign appearances and did the rounds of entertainment television shows to talk about her initiatives against childhood obesity, the organic vegetable garden she has planted at the White House and her support for military families. Just as crucially in such an expensive contest, Mrs Obama kept a busy schedule of lucrative fund-raisers with donors. The First Lady is hugely popular with the party faithful and has an across-the-board approval rating of nearly 70 per cent, much higher than her husband’s.

While their mother’s involvement was highly public, Malia and Sasha were assigned an important supporting role, usually unseen but often cited, in their father’s campaign – such as the one they had on that cold night last week in Des Moines.

Both parents invoked them frequently as they discussed what sort of future Mr Obama envisaged for America and the president did not shy away from quoting their views on policy when he wanted to make a point that he apparently felt was evident even to a child. The Obamas also regularly dropped in homely nuggets about family life with the girls.

It is a fine and at times controversial line to walk between endearing and exploitative. Indeed, the Obamas themselves have admitted that they regretted allowing their then much-younger girls to be interviewed on television alongside their parents when Mr Obama first ran for the presidency.

During their first four years at the White House, the couple have been fiercely protective of their daughters’ privacy, despite frequently mentioning them in speeches and interviews.

Mr Obama’s triumph on Tuesday now means that they will have arrived in the White House as children, aged nine and six, and will not leave until they are teenagers heading into adulthood, with all the scrutiny that a president’s children can expect.

“Sasha and Malia, before our very eyes, you’re growing up to become two strong, smart, beautiful young women, just like your mum,” noted Mr Obama proudly during his victory speech.

In a perk of life as first daughters, they had been flown in to Chicago after a regular day at school in Washington with their grandmother Marion Robinson, who lives in the White House and stands in for their mother when the First Lady is away.

But that life has its downsides too. Unlike many girls her age, Malia is not allowed a Facebook page by her father for security reasons and future boyfriends may find her chaperones a tad intimidating.

“Dates, that’s fine, she’s got Secret Service protection,” Mr Obama joked in a recent interview, though he said that there had not been “anything official” yet in terms of boyfriends.

In his speech in Chicago, Mr Obama also delivered a tribute to his wife. “I wouldn’t be the man I am today, without the woman who agreed to marry me 20 years ago,” he said. “Let me say this publicly. Michelle, I have never loved you more. I have never been prouder to watch the rest of America fall in love with you too as our nation’s First Lady.”

Given that his electoral victory in several swing states owed much to his strong support among women, he had good reason to be grateful for her appeal to female voters.

But it has been a rollercoaster ride to popularity for Mrs Obama since her husband first ran for the presidency. Then she struggled with verbal missteps, most notably when she implied that she had not always been proud of America – ill-chosen words that continued to provide campaign fodder against Mr Obama.

She came under criticism during his first term for her penchant for foreign holidays and her spending on decor at the White House.

And earlier this year a new book challenged the White House portrayal of her as a charming and diplomatic First Lady who supports her husband’s administration with such uncontroversial measures as her healthy living initiative.

Rather, she battled with her husband’s advisers for influence over policies such as health-care reform, according to The Obamas by Jodi Kantor, a respected New York Times reporter.

But for many Americans, her most obvious role is as a sartorial icon with a wardrobe that mixes high street and designer fashions, often featuring sleeveless tops and dresses that show off her famously toned arms.

And for Wednesday night’s celebrations, she donned a magenta silk crêpe de Chine dress by the designer Michael Kors that she first wore in 2010 – a nod to recycling in these difficult economic times – accompanied by a black cardigan and black heels.

As the girls have matured, so their fashion choices are also coming under the spotlight. Both wore striking outfits on Wednesday – Malia in an electric-blue, A-line skirt with a pink, studded belt; and Sasha in an abstract-print green skirt, grey bow-front top and shrunken cardigan – that fashion-watchers noted mimicked their mother’s look.

Away from the politics and the fashion, Mrs Obama has always insisted that her overwhelming priority is bringing up her daughters and still refers to herself by the rather cloying title of “mom-in-chief” that she adopted back in 2008.

But by the time she and her husband leave the White House in 2017, Malia will be heading off to college and Sasha will be well into her high school years.

The Harvard Law School graduate and high-flying career woman who reluctantly gave up her job as a hospital executive to campaign for her husband in 2007 will no longer be “mom” in the same way.

Mrs Obama’s friends have laughed off suggestions that she could become the new Oprah Winfrey, the chat show queen. But after twice helping deliver the presidency to her husband, no one who has followed her progress from the working-class South Side of Chicago to the country’s most famous address is in any doubt that the First Lady will want to take on an ambitious new role.